Work around issue with old (<2.0) cabal versions and the hackage index.

Actually the issue is worked around on hackage-side, but it seems not in
the fpcomplete mirror.
See haskell/cabal#4624 (comment).

.travis.yml

@@ -109,9 +109,12 @@ before_install:
     unzip -j protoc-*-linux-x86_64.zip bin/protoc -d ~/.local/bin
   fi
 
+  # Temporary use normal hackage, as it might have cabal workarounds, see
+  # https://github.com/haskell/cabal/issues/4624#issuecomment-318743713.
   # Use the more reliable S3 mirror of Hackage
   mkdir -p $HOME/.cabal
-  echo 'remote-repo: hackage.haskell.org:http://hackage.fpcomplete.com/' > $HOME/.cabal/config
+  # echo 'remote-repo: hackage.haskell.org:http://hackage.fpcomplete.com/' > $HOME/.cabal/config
+  echo 'remote-repo: hackage.haskell.org:http://hackage.haskell.org/' > $HOME/.cabal/config
   echo 'remote-repo-cache: $HOME/.cabal/packages' >> $HOME/.cabal/config
 
   if [ "$CABALVER" != "1.16" ]